Techniques are known for removing noise from digital representations of data images obtained by digitally scanning documents and the like. The scanned documents are processed to identify objects within the scanned images that are, in turn, used to mask out the noise. For example, U.S. Pat. No. 7,016,536 discloses a method and apparatus for removing noise by building objects from reduced resolution representations of the scanned image and including the identified objects in a mask that is logically ANDed with the de-skewed representation of the scanned document. Objects identified as picture objects are included in a mask and logically ANDed with the de-skewed representation to eliminate all other objects, while objects marked as data objects are added to the representation to provide a de-skewed, de-speckled representation of the scanned document.
Digital signal processing techniques are well-known that may be used to provide contrast enhancement. For example, Pratt discloses in “Digital Image Processing,” Third Edition, pp. 253-262, a traditional method for contrast adjustment. Unfortunately, the dark scanning borders that may occur around the border area where the scanner sensor was not covered by paper create spikes in the histogram of the image, which makes such traditional contrast adjustment unreliable. A method and digital signal processing apparatus are desired that improves the quality of the contrast adjustment for documents with a dark scanning border. The present invention satisfies such needs in the art.